1. Field of the Invention
The present invention relates to a chemical vapor deposition device for manufacturing semiconductor devices. More particularly, the present invention relates to a view port of the chemical vapor deposition device that allows the chemical vapor deposition process to be observed from outside the process chamber.
2. Description of the Related Art
Chemical Vapor Deposition (CVD) is a process in which a wafer surface is coated with a compound. CVD systems are classified as atmospheric pressure CVD systems, low pressure CVD systems, and high pressure CVD systems depending on the pressure used during the process performed thereby.
In addition, Plasma Enhanced CVD (PECVD) is a low pressure deposition process in which gaseous neutral molecules are bombarded with highly-accelerated electrons, produced by glow discharge, whereby the molecules decompose and assume the state of plasma. The molecules of the plasma are deposited on a surface of a substrate under a chemical reaction with the material thereof.
As shown in FIG. 1, a PECVD apparatus requires a pair of electrodes 1, 2 to form the plasma. The electrodes 1, 2 are supplied with high frequency power, to thereby create plasma out of the gaseous molecules filling a process chamber 3. The molecules of the plasma are then deposited on a surface of the wafer 4 supported within the process chamber 3.
The electrodes 1, 2 serve to form the walls of the process chamber 3 and to emit high frequency power. The electrode 2 also defines openings therein at which a plurality of view ports 5 are provided. These view ports 5 are disposed at the same height as or higher than the wafer 4 supported in the chamber. The view ports 5 are made of transparent material. In particular, the view ports include a pane of transparent material 5a (hereinafter referred to merely as a xe2x80x9cwindowxe2x80x9d) that allows a user to see inside the chamber 3 and thereby obtain information regarding the progress of the PECVD process.
The PECVD apparatus also includes a vacuum port 6. In PECVD, the chamber 3 must always contain a constant amount of gas. Any gas in the chamber 3 in excess of that constant amount is discharged from the chamber through the vacuum port 6. The vacuum port 6 also allows impurities created as the result the process to be discharged from the chamber together with the excess process gas.
The impurities discharged through the vacuum port 6 include some polymer created when the plasma is formed. Most of the polymer, however, is deposited on the inner surfaces of the electrodes 1, 2. Such polymer is removed regularly from the electrodes 1, 2 in a cleaning process. The polymer is also deposited on the inner surfaces of the view ports 5. The surface temperatures of the windows 5a and the electrodes 1, 2 differ due to their being made of different materials. Accordingly, more polymer is deposited on the inner surfaces of the windows 5a than on the inner surfaces of the electrodes 1, 2. The polymer eventually falls from the inner surfaces of the windows 5a onto the wafer 4, causing the manufacturing process to fail.
In addition, the polymer deposited on the inner surface of the transparent window 5a makes it is impossible to see inside the chamber 3.
In order to prevent the polymer from adhering to the inner surface of the window of the view port or to remove the polymer once it adheres to the surface, Japanese Patent Publication No. Hesei 3-050723 proposes heating the window using an alloy ire or using a structure that directs dry warm air onto the surface. Japanese Patent Publication No. Hesei 8-246148 discloses a transparent window made of acryl resin, polyester resin, epoxy resin, polycarbonate resin, or polyamide resin, that resists the tendency of polymer to adhere thereto. In addition, Japanese Patent Publication No. Hesei 11-204294 discloses a heater provided on a window of a view port to prevent impurities from accumulating on the window. However, integrating the window with an alloy wire or an air guiding structure is very difficult. In addition, the alloy wire and the heated air dirty the window rather quickly, making it very difficult to see inside of the chamber 3.
Japanese Patent Publication No. Hesei 9-196059 discloses a transparent window coated with Teflon, a polymer of the fluorine series, or a heat-resistant rubber. Providing the window with an anti-corrosion material may protect the window, but does not serve to prevent the polymer from adhering to the window or to remove the polymer once it becomes adhered to the window. On the other hand, the requirements of a film capable of preventing the polymer from adhering to the window are rather severe, i.e., the film must be of a transparent material as well as be resistant to high temperatures.
An object of the present invention is to overcome the above-described technical problems associated with the prior art. More specifically, the object of the present invention is to provide an economical and effective view port by which the inside of the chamber can be readily observed and yet by which heat loss through the window thereof is prevented, thereby suppressing the tendency of polymer to adhere to the window surface.
To achieve this object, the view port of the chemical vapor deposition device of the present invention includes a bracket protruding from the outside of the chamber and extending around an opening formed in an electrode serving as a wall of the chamber, the bracket having an opening therethrough, a window held by the bracket against the wall via an O-ring, a cap for capping the opening of the bracket; one side of the cap being connected to one side of the bracket with a hinge, the other side of the cap detachably connected to the bracket by a locking member, whereby the cap is movable between open and closed positions, and heat loss-preventing means integral with the cap for preventing heat loss at the window.
The heat-loss preventing means can be a body of heat-insulating material attached to or making up a substantial part of the cap. The heat-loss preventing means can also comprise a heater element, such as a resistive heating element or a warm air duct, discrete from the window but disposed close to the front surface thereof, and integral with the cap. When the cap is opened, the heat loss-preventing means is moved away from the front surface of the window so that the inside of the chamber can be observed. However, when the cap is closed during the deposition process, the heat loss-preventing means is held close to the front surface of the window and serves to maintain the high temperature state of the window. With the window maintained at a high temperature, impurities created during the deposition process can not adhere thereto.